Earth’s vegetation could be saturated with carbon by the end of the century and stop acting as a brake on global warming, scientists warn.

A 4C rise in global temperature, predicted by 2100, marks the threshold point after which terrestrial trees and plants will be unable to soak up any more carbon from the atmosphere.

Atmospheric carbon will then start to increase more rapidly, accelerating climate change, the researchers warn.

Vegetation acts as a "carbon sink", a natural system that takes carbon dioxide from the air and traps it. The Amazon rain forest and the
vast belt of coniferous Boreal forest that rings the northern hemisphere both act as powerful carbon sinks.

Initially, higher levels of carbon dioxide in the atmosphere will stimulate more plant growth. But the impact of a warmer world will gradually counterbalance this trend until saturation point is reached, say the scientists.

Global warming of 4C will result in the Earth's land vegetation becoming dominated by negative effects, such as "moisture stress", caused by plant cells getting too little water.

At this point, further absorption of atmospheric carbon is likely to flatline, according to the research published in the journal Proceedings of the National Academy of Sciences.